The 2004 deal was just one part of a revolving-door relationship between the agency and the private security firm. Use of outside contractors for such activities has come under widespread criticism.

WASHINGTON — The CIA's decision to hire contractors from Blackwater USA for a covert assassination program was part of an expanding relationship in which the agency has relied on the widely criticized firm for tasks including guarding CIA lockups and loading missiles on Predator aircraft, according to current and former U.S. government officials.

The 2004 contract cemented what was then a burgeoning relationship with Blackwater, setting the stage for a series of departures by senior CIA officials who took high-level positions with the North Carolina security company.

The revolving door helped fuel a backlash against what many inside the agency and on Capitol Hill came to regard as an overuse of outside firms, many of which made millions of dollars after filling their staffs with former CIA employees.

"I have believed for a long time that the intelligence community is over-reliant on contractors to carry out its work," said Sen. Dianne Feinstein (D-Calif.), chairwoman of the Senate Intelligence Committee. "This is especially a problem when contractors are used to carry out activities that are inherently governmental."

Her comment underscored how the Blackwater contract's disclosure has renewed questions about the sort of work the CIA has outsourced since the Sept. 11 attacks. In recent years, the agency has also faced criticism for using contractors to interrogate prisoners.

Experts said that there may not be any legal barrier against using contractors to kill terrorism suspects or subject them to brutal interrogations. Still, they said, there tends to be deep public discomfort with the idea of delegating certain activities -- whether issuing pardons, making arrests or pulling triggers -- to people who are not direct government employees.

"The use of force has been traditionally thought of as inherently governmental," said Jeffrey Smith, former CIA general counsel. "The use of a contractor actually employing lethal force is clearly troublesome, but I'm not sure it's necessarily illegal."

U.S. officials familiar with the targeted-killing program said that Blackwater's involvement was limited in scope and duration, and that the arrangement ended several years before CIA Director Leon E. Panetta killed the program two months ago.

The program was kept secret from Congress for nearly eight years before Panetta told lawmakers about it in June. CIA officials have emphasized that the program was never operational and that it did not lead to the capture or killing of a single terrorism suspect.

"It was never successful, so he ended it," CIA spokesman Paul Gimigliano said. Panetta "never suggested to Congress that anyone at the CIA misled the intelligence committees or otherwise broke the law."

The CIA delivered a report to Congress earlier this month after conducting an internal investigation of the program, which was launched after the Sept. 11 attacks but was canceled and restarted several times under different regimes at the agency.

Officials familiar with the report said that the agency did not have a formal contract with Blackwater in connection with the targeted-killing program. Instead, the agency hired the company's founder, Erik Prince, a former Navy SEAL, and other Blackwater executives to help turn an idea for forming Al Qaeda hit squads into an operational program.

The effort ranged from consulting with top executives to carrying out training exercises at Blackwater's headquarters in North Carolina. Company officials did not respond to requests for comment.

Blackwater was also closely associated with the CIA's Predator aircraft operations, one of the most successful weapons in the agency's arsenal against the Al Qaeda terrorist network. Former CIA officials said that from the beginning, Blackwater provided security at the air base in Shamsi, Pakistan, where the Predator aircraft were based.

At the time, the company that manufactures the drone, General Atomics, was responsible for loading the Hellfire missiles used to target dozens of Al Qaeda leaders. But that task was subsequently switched to Blackwater, sources said.

The agency "has always used contractors," said a former CIA official familiar with the Predator operations. "You have to be an explosives expert," and the CIA has never sought to use its own personnel for the highly specialized task. "We didn't care who put on the munitions as long as it wasn't CIA case officers," the former official said.

Gimigliano declined to comment on Blackwater's involvement with Predator, saying the CIA "as a rule does not deny or confirm reports on contractual relationships."

Blackwater changed its name to Xe Services LLC to escape the notoriety that followed a series of bloody incidents in Iraq, where the firm was accused of employing excessive force while providing protection for State Department employees. In one case, Blackwater guards were accused of opening fire in a crowded Baghdad square and killing 17 civilians.